Spondylolisthesis is the anterior or posterior displacement of a vertebra or the vertebral column in relation to the vertebrae below. The variant "listhesis," resulting from misdivision of this compound word, is sometimes applied in conjunction withscoliosis. These "slips" (aka "step-offs") occur most commonly in the lumbar spine. Spondylolysis (a defect or fracture of the pars interarticularis of the vertebral arch) is the most common cause of spondylolisthesis. This is not to be confused with a slipped disc, where one of the spinal discs in between the vertebrae has ruptured.

A hangman's fracture is a specific type of spondylolisthesis where the C2 vertebra is displaced anteriorly relative to the C3 vertebra due to fractures of the C2 vertebra's pedicles.

Classification
Spondylolisthesis is officially categorized into five different types:.

• Dysplastic spondylolisthesis is a rare congenital spondylolisthesis occurring because of a malformation of the lumbosacral junction resulting in small, incompetent facet joints.
• Isthmic spondylolisthesis is the most common form of spondylolisthesis. Isthmic spondylolisthesis (also called spondylolytic spondylolisthesis) is a common condition with a reported prevalence of 5–7 percent in the US population. A slip or fracture of the intravertebral joint is usually acquired between the ages of 6 and 16 years, but remains unnoticed until adulthood. Roughly 90 percent of these isthmic slips are low-grade (less than 50 percent slip) and 10 percent are high-grade (greater than 50 percent slip).
• Degenerative spondylolisthesis is a disease of the older adult that develops as a result of facet arthritis and joint remodeling. Joint arthritis, and ligamentum flavum weakness, may result in slippage of a vertebrae. Degenerative forms are more likely to occur in women, persons older than fifty, and African-Americans.
• Traumatic spondylolisthesis is very rare and results from acute fractures in various areas of the neural arch, other than the pars.
• Pathologic spondylolisthesis has been associated with damage to the posterior elements from metastases or metabolic bone disease. These slips have been reported in cases of Paget's disease of bone, tuberculosis, giant-celltumors, and tumor metastases.